Evaluation of Bioactivities of Bovine Milk Osteopontin Using a Knockout Mouse Model

Osteopontin (OPN) is a multifunctional protein present abundantly in human milk, but at low levels in bovine milk and infant formula. Bovine milk OPN (bmOPN) is commercially available, and may therefore, be added to formula. OPN exerts its multiple functions by binding to its receptors to activate cell signaling pathways. The OPN receptor (integrin)-binding site is conserved across species; therefore, bmOPN may exert bioactivities in humans and mice. The objective of the present study was to evaluate bioactivities of bmOPN using an established OPN knock-out (KO) mouse model.We evaluated bioactivities of bmOPN, including effects on intestinal growth, immune response, and brain development. In the present study, wild-type (WT) pups were nursed by WT dams, KO dams, or KO dams with bmOPN supplementation from postnatal days 1 to 21 (P1--P21).Our results show that orally ingested bmOPN is partly resistant to in vivo gastrointestinal digestion, and supplemental bmOPN exhibited similar effects as mouse milk OPN (mmOPN) on promoting growth of the small intestine revealed by histological analysis of duodenum villus height and crypt depth at P10, on modifying TNF-α response against a LPS challenge at P30, as well as promoting brain myelination by increasing expression of myelin-associated glycoprotein (MAG) and myelin basic protein (MBP) and improving cognitive development.Our finding that bmOPN with an amino acid sequence different from mmOPN but with a conserved integrin binding site exerts bioactivities similar to mmOPN suggests that bmOPN may provide bioactivities to human infants when added to formula.